Biodiversity Journal, 2020,11 (4): 1045–1053 https://doi.org/10.31396/Biodiv.Jour.2020.11.4.1045.1053

New data on the seasonality of affinis (Gmelin, 1791) and peregrina (Gmelin, 1791) ( Nudi- branchia) in the Ionian Sea, Central Mediterranean

Andrea Lombardo* & Giuliana Marletta

Department of Biological, Geological and Environmental Sciences - Section of Biology, University of Catania, via Androne 81, 95124 Catania, Italy *Corresponding author: [email protected]

ABSTRACT (Gmelin, 1791) and (Gmelin, 1791) are two common nudibranchs in the Mediterranean Sea. However, there are only a few studies on their season- ality which reported these principally in summer and in well-lit shallow areas. Instead, through the present study carried out throughout three years (from 2017 to 2019) in three areas sited along the Ionian coast of Sicily (Italy), it has been observed that: 1) both species may be present in any season of the year with a high number of specimens; 2) F. affinis in the study areas is more competitive than C. peregrina; 3) both species showed a less photophilous lifestyle than that usually reported in literature, since in this study both species were found in a deeper bathymetric range; 4) F. affinis and C. peregrina could be considered warm-water species and their strong presence in cold seasons might be used as an indicator of the increase in the seawater temperature of the Mediterranean Sea.

KEY WORDS Cratena peregrina; Flabellina affinis; Ionian Sea; Nudibranchia; seasonality.

Received 30.08.2020; accepted 01.12.2020; published online 30.12.2020

INTRODUCTION eggs of this species usually are produced in a tangle with a pink-violet colouring (Figs. 2, 3) (Trainito & Flabellina affinis (Gmelin, 1791) and Cratena Doneddu, 2014). peregrina (Gmelin, 1791) are two nudibranchs of Also C. peregrina (Fig. 5) is a common the family and , species, distributed in the Mediterranean and along respectively. Flabellina affinis (Fig. 1) is a common the Atlantic coasts of Iberian Peninsula and in species, distributed in the Mediterranean Sea, along Canary Islands (Trainito & Doneddu, 2014). C. the Atlantic African coasts and Canary Islands peregrina has a white transparent body with (Trainito & Doneddu, 2014; Ballesteros et al., arranged in 9 groups on each side of the back. The 2012–2020). This species is irregularly pink cerata can be long as the , which are coloured with from six to nine ceratal clusters on smooth and cylindrical. The oral tentacles are each side of the back. Each ceratal cluster originates twice as long as the rhinophores. From the base of from a peduncle, which divides in several branches. oral tentacles to the base of the rhinophores, on Rhinophores have from 17 to 36 annulations and each side of the head there is an evident orange oral tentacles are shorter than cerata and almost spot (Schmekel & Portmann, 1982). The eggs of long as rhinophores (Schulze & Wägele, 1998). The C. peregrina are produced in a tangle which can 1046 ANDREA LOMBARDO & GIULIANA MARLETTA

be whitish-pink coloured (Figs. 6, 7) (Trainito & summer, which disappears in autumn and reappears Doneddu, 2014). the next summer. F. affinis usually feeds on some Flabellina affinis is a photophilous species, species of hydrozoans such as reported on different habitats: among photophilous glomeratum Picard, 1952, E. racemosum, E. seaweeds in rocky coasts, in the coralligenous ramosum (Haefelfinger, 1960; Ros, 1975; Barletta biocenosis, in Zostera meadows, on sandy bottoms, & Melone, 1976; Schmekel & Portmann, 1982; on encrusting sponges, rarely on Posidonia Hirano & Thompson, 1990; McDonald & oceanica (Linnaeus) Delile, 1813 and frequently on Nybakken, 1997; Betti, 2011, Trainito & Doneddu, hydrozoans [particularly on 2014). (Linnaeus, 1758) and Eudendrium racemosum Similarly, C. peregrina is a photophilous species (Cavolini, 1785)]. Sometimes, F. affinis can be also which was reported on different types of substrates: found in dark cavities and on deep bottoms, even on rocky coasts, among seaweeds at 20 m depth, in though this species was reported in lighted areas P. oceanica and Zostera meadows, at caves’ near the surface (Ros, 1975; Barletta & Melone, entrance, on sandy bottoms, rarely in coralligenous 1976). Concerning its seasonality, according to Ros biocenosis and frequently on Eudendrium spp. (1975), F. affinis is abundant during summer along (particularly on E. ramosum and E. racemosum with other species such as C. peregrina and colonies in well-lit vertical walls) (Ros, 1975; banyulensis Portmann & Sandmeier, 1960. Barletta & Melone, 1976). Ballesteros (1980) Moreover, Ballesteros (1980), in his faunistic study reported that C. peregrina is particularly distributed on nudibranchs and sacoglossan of Catalan coasts, in a range of depth of 0–10 m. According to Betti reported that F. affinis is a prevalently summer (2011), in the area of Conero this species is very species and its principal bathymetric range is abundant and particularly frequent on well-lit rocky between 5–10 m. According to Betti (2011), in the bottoms, also in shallower waters, on Eudendrium area of Conero (Adriatic Sea), F. affinis, with C. spp. colonies and it spawns at the beginning of peregrina, is a species very frequent during summer. Furthermore, in this area, C. peregrina is

Figures 1–4: Flabellina affinis from the central-eastern coasts of Sicily. Fig. 1: lateral view of a F. affinis specimen. Fig. 2: F. affinis eggs on Eudendrium sp. Fig. 3: a F. affinis specimen during spawning on Eudendrium sp. Fig. 4: two specimens during breeding (photos A. Lombardo). New data on the seasonality of Flabellina affinis and Cratena peregrina (Nudibranchia) in the Ionian Sea 1047

present from the late spring to the beginning of three years (from 2017 to 2019) in different sites autumn (Betti, 2011). located along the central-eastern coast of Sicily Cratena peregrina usually feeds on different (Italy) (Figs. 9, 10). The sites were selected basing hydrozoans: (Pallas, 1766), on different environmental conditions. Two sites, E. racemosum, E. ramosum, Pennaria disticha Ognina (37°31’50.4”N – 15°07’10.8”E) and Goldfuss, 1820, Pennaria spp. e Tubularia spp. Bellatrix (37°32’03.2”N – 15°07’35.2”E) are both (Haefelfinger, 1961; Ros, 1975; Barletta & Melone, located in the municipality of Catania and are the 1976; Schmekel & Portmann, 1982; McDonald & most anthrophized sites among the study areas. Nybakken, 1997; Betti, 2011; Trainito & Doneddu, Since they have the same environmental 2014). conditions and are situated close to each other, Although F. affinis and C. peregrina are very were considered as a single site, listed from now common and easily observable species in the on as “Catania”. Two sites, “Scalo Pennisi” Mediterranean Sea, data on their seasonality are (37°38’23.2”N – 15°11’04.6”E) and “Acque scarce, particularly in the Ionian Sea. Indeed, Fredde” (37°38’15.7”N – 15°10’52.1”E), are both information on the seasonality of these two situated in the hamlet of Santa Tecla, in the species came only from the Catalan coasts of municipality of Acireale. These sites are the least Spain (Ros, 1975) and the Adriatic Sea (Betti, polluted among the study areas. Therefore, since 2011). The aim of the present research is to gain they have similar environmental conditions and knowledge on seasonality of F. affinis and C. are close to each other, they have been considered peregrina along the central-eastern coast of Sicily as a single site and listed from now on as “Santa (Ionian Sea). Tecla”. Finally, the last study station was Santa Maria La Scala (37°36’46.5” N – 15°10’31.4”E), MATERIAL AND METHODS in the municipality of Acireale, which has intermediate conditions between those of Catania This study has been carried out throughout and Santa Tecla and, thus, was considered

Figures 5–8: Cratena peregrina from central-eastern coasts of Sicily. Fig. 5: lateral view of a C. peregrina specimen. Fig. 6: C. peregrina eggs on Eudendrium sp. Fig. 7: a C. peregrina specimen with eggs on Eudendrium sp. Fig. 8: two specimens before breeding (photos A. Lombardo). 1048 ANDREA LOMBARDO & GIULIANA MARLETTA

Figures 9, 10: Study area. Fig. 9: eastern coast of Sicily. Fig. 10: study sites within the central-eastern coast of Sicily. individually. Both Santa Maria La Scala and RESULTS Santa Tecla present several springs due to the flow of freshwater from the Etna to the sea Catania (Figs. 11, 12) (Ferrara, 1977; Catra et al., 2006). Data were collected through underwater visual census with Catania was the site with the highest average scuba diving. In particular, a total of 224 dives has number of F. affinis specimens, throughout the three been realized: 74 in Santa Maria La Scala, 83 in years of study. During 2017, winter represented the Catania (Bellatrix and Ognina), 67 in Santa Tecla season with the maximum average number of found (Scalo Pennisi and Acque Fredde). Each scuba specimens (27.83). The other seasons presented the dive (in a range of depth of about 0–45 m, same trend (f), which was different than the winter according to the seabed geomorphology) was trend. Indeed, between winter and the other seasons, conducted all year round (marine-weather there was a decrease of -78.87% (p<0.01) in the conditions permitting), twice a week, during average number of specimens. During 2018, each daylight, between 9–11:30 am. For each site, the season presented a different trend. In fact, winter same path was followed and F. affinis and C. had the highest average number of specimens (36), peregrina specimens were photographed with an while autumn was the season with the lowest Olympus TG–4 underwater camera and counted average number of specimens (5). Between these in situ. For each station and for each species, the seasons there was a reduction of -86.11% (p<0.01). average minimum depths and the average In spring, there was a reduction in the average maximum depths, in which the specimens were number of specimens, while in summer there was a encountered, have been obtained. slightly increase (21.66). During 2019, there was The seasons were considered as follows: winter the most stable seasonal trend than the previous (December, January, February), spring (March, April, years. During this year, winter was the season with May), summer (June, July, August) and autumn the highest average number of specimens (19.66), (September, October, November). Through data while autumn was the season with the lowest collection, the demographic trend of both species average number of specimens (8.66). Between was assessed. In addition, for each station, specific winter and autumn, there was a decrease of -55.95% density was evaluated as mean number of (p<0.01). Spring and summer presented the same individuals/diving number per site. The experimental trend (e). In Catania, F. affinis specimens were design adopted was completely randomized and found at an average depth-range of 16.5–32.1 m. replicated four times. Data were subjected to analysis Concerning the breeding and spawning activities of variance (ANOVA). Mean comparisons were (Figs. 3, 4), during 2017 they were observed in any performed according to Tukey Minimal Difference season of the year. In 2018, the eggs were found all (MDS). year round, while the breeding activity was New data on the seasonality of Flabellina affinis and Cratena peregrina (Nudibranchia) in the Ionian Sea 1049

documented in winter, spring and summer. In 2019, number of individuals among all year of study the eggs were seen throughout all year, while the (9.66). Between summer and autumn, there was an breeding activity was observed in summer and increase of 190% (p<0.01). In the site of Catania, autumn. C. peregrina specimens were averagely found in the Regarding C. peregrina, in this site the seasonal bathymetric range of 9.7–25.8 m. With regard to C. trends were all different in each year of study, with peregrina eggs (Fig. 6–7), they were found during an almost stable presence of a low average number 2017 in summer and autumn, in 2018 they were of individuals. During both 2017 and 2018, a rather observed in winter, summer and autumn, in 2019 steady and similar population trend has been they were documented in all seasons. For this observed, with the exception of spring 2017 in species, the breeding activity (Fig. 8) was seen only which the lowest average number of specimens has in the winter 2018. been found (1.00). Indeed, between winter and spring 2017, there was a decrease of -75.96% Santa Maria La Scala (Figs. 13, 14) (p<0.01) of the average number of specimens. During 2019, contrary to the previous years, winter Santa Maria La Scala was the site with an presented the least average number of individuals. average number of F. affinis specimens which was In this year, spring and summer showed a similar intermediate between the values observed for trend with a slightly higher average number of Catania and Santa Tecla. During 2017, winter was specimens. In 2019, autumn had the highest average the season with the highest average number of

Figure 11. Oscillations in the average number of F. affinis Figure 12. Oscillations in the average number of C. specimens found in Catania during the three years’ trial. peregrina specimens found in Catania during the three Different letters indicate differences at p<0.01. years’ trial. Different letters indicate differences at p<0.01.

Figure 13. Oscillations in the average number of F. affinis Figure 14. Oscillations in the average number of C. peregrina specimens found in Santa Maria La Scala during the three specimens found in Santa Maria La Scala during the three years’ trial. Different letters indicate differences at p<0.01. years’ trial. Different letters indicate differences at p<0.01. 1050 ANDREA LOMBARDO & GIULIANA MARLETTA

found individuals (12.17). Summer and autumn had average number of found specimens was spring the same trend, similar to the winter trend. Instead, (1.00). Between spring and summer-autumn there spring was the season with the lowest average was an increase of 641% (p<0.01) in the average number of specimens (5.33). Between winter and number of F. affinis specimens. During 2018, there spring there was a decrease of -56.20% (p<0.01). was a more stable seasonal trend and only in spring Oppositely, during 2018, the season with the there was a slight decrease. Instead, during 2019, greatest average number of individuals was spring almost all seasons, except for winter and autumn, (14.00), while that with the lowest average number presented different trends. Between winter and of specimens was winter (8.33). Between winter summer, the season with the greatest average and spring there was an increase of 68.06% number of specimens, there was an increase of (p<0.01). As in 2017, also in 2018, summer and 200.42% (p<0.01). In Santa Tecla, on average, F. autumn had the same trend. Instead, during 2019, a affinis specimens were found in the bathymetric sharp decline of -95.81% in the average number of range of 16.6–26.1 m. In this site, during 2017, F. F. affinis specimens occurred between winter and affinis eggs were found in spring and autumn. In autumn. In Santa Maria La Scala, F. affinis 2018, the eggs were observed throughout all specimens were averagely found in a bathymetric seasons, while the breeding activity was range of 19.6–34.8 m. In this study area, the documented only in winter. During 2019, the eggs breeding and spawning activities were documented were found in spring, summer and autumn. in all seasons during 2017. In 2018, the eggs were In Santa Tecla, during each year of study, a found all year round and the breeding activity was different seasonal trend of C. peregrina has been observed in winter and spring. During 2019, the observed. During 2017, there was an identical trend eggs were found in spring, summer and autumn and for winter and summer (d), and two different trends no breeding activity was observed. for spring and autumn. Between winter and spring In Santa Maria La Scala, during each year of there was a decrease of -47.31% (p<0.01), while study, the seasonal trends of C. peregrina were between summer and autumn there was a reduction different. In 2017, two main trends were observed: of -66.66% (p<0.01) in the average number of one identical for winter and summer (b) and another specimens. During 2018, each season presented a equal for spring and autumn (e). Each passage from different trend of the average number of C. trend (b) to trend (e) was signed by a decrease of - peregrina individuals. After a decrease of -91.75% 62.17% (p<0.01). During 2018, there was a more (p<0.01) occurred between winter and spring, the stable trend of the average number of C. peregrina season with the lowest average number of found specimens with a decrease from winter to autumn specimens in this site, there was an increase of of -50% (p<0.01). During 2019, there was a winter 2830% (p<0.01) in autumn, the season with the peak (8.33) and sharp decline in summer (1.00) of highest average number of found specimens. the average number of specimens. From winter to Instead, during 2019, there were two distinct trends: summer, a decrease of -87.99 % (p<0.01) was one equal for winter and summer (e) and another observed. In this site, on average, C. peregrina identical for spring and autumn (b). Between these specimens were observed in a depth-range of 12.4 trends there was an increase of 154.62% (p<0.01) –33.5 m. Furthermore, C. peregrina eggs were in the average number of specimens. In Santa Tecla, found in all seasons during both 2017 and 2018, C. peregrina specimens were averagely found in the while throughout 2019 they were seen in winter, bathymetric range of 11.4–19.6 m. Regarding C. spring and summer. peregrina eggs, they were found during 2017 only in summer, during 2018 in summer and autumn and Santa Tecla (Figs. 15, 16) in all seasons of 2019.

Santa Tecla was the study area with the lowest average number of F. affinis specimens (4.86). DISCUSSION During 2017, the seasons with the highest values of the average number of specimens were summer and In the present study the seasonality of two autumn (~7.40), while the season with the lowest common eolidacean nudibranchs, F. affinis and C. New data on the seasonality of Flabellina affinis and Cratena peregrina (Nudibranchia) in the Ionian Sea 1051

Figure 15. Oscillations in the average number of F. affinis Figure 16. Oscillations in the average number of C. specimens found in Santa Tecla during the three years’ trial. peregrina specimens found in Santa Tecla during the three Different letters indicate differences at p<0.01. years’ trial. Different letters indicate differences at p<0.01. peregrina, has been investigated throughout three and hydrozoans (Betti, 2011). Consequently, F. years (from 2017 to 2019), in three areas along the affinis and C. peregrina populations in this station central-eastern coast of Sicily. During the data during 2019 may have been decimated by collection, it has been observed that these species competition and predation caused by D. banyulensis. were present in all seasons and years. Probably, the Generally, in all study areas, the number of F. presence of F. affinis and C. peregrina all year round affinis specimens was greater than the number of C. could be related to the presence, in all study areas, peregrina specimens. There are two main of E. racemosum and E. glomeratum, which hypotheses that could explicate this trend: in the alternate during the year. In fact, according to study sites F. affinis might be a more competitive Bavestrello et al. (2006), E. racemosum colonies are species than C. peregrina, otherwise the larval active from April and are fertile during the summer, recruitment of F. affinis is higher than the degenerating in the autumn, while E. glomeratum is recruitment of C. peregrina. Furthermore, it has a winter species that appears in mid-October and been observed that the number of F. affinis decreases until April (Boero, 1984). Consequently, specimens, increase southwards and, thus, Catania since these hydrozoans constitute the diet of both F. was the study area with the highest average number affinis and C. peregrina, these nudibranchs may of individuals. This event could depend on the fact have the food resources available all year round. that allochtnous-produced larvae of F. affinis might Moreover, the presence in some seasons of a higher be carried through the powerful Algerian Current or lower number of specimens of these species, (Di Silvestro et al., 2010), coming from the could depend on a major or minor larval southern Mediterranean and thus, Catania, among recruitment. Indeed, according to Clark (1975), the the studied areas, is the site with the greatest sudden appearances of population often are due to recruitment. The same behaviour was not observed the arrival of large numbers of allochtnous-produced for C. peregrina, whose average number of larvae, that is related to critical temperatures that specimens was almost identical for each site. stimulate settling and metamorphosis. Furthermore, However, we believe that generally the allochtnous- the decrease in the number of specimens of these produced larvae of both species could be species could also depend on the presence of transported by the modified Atlantic water (MAW) predators. In particular, during 2019 in the site of flow from the western Mediterranean Sea otherwise Santa Maria La Scala, we observed a strong through the Levantine intermediate water (LIW) decrease in the populations of both F. affinis and C. flow form the eastern Mediterranean Sea peregrina, concomitantly with the increase in the (Pirkenseer, 2013). Through data collection, it has number of specimens of another species, been seen that the F. affinis depth-range begins D. banyulensis in the same bathymetric range of the deeper than the bathymetric range of C. peregrina, examined species (personal observations). Indeed, which it has also been observed in shallower waters. D. banyulensis is a predator of other nudibranchs These data are different than those reported in the 1052 ANDREA LOMBARDO & GIULIANA MARLETTA

literature cited above (Ros, 1975; Barletta & coasts of Sicily is more abundant, and probably Melone, 1976; Ballesteros, 1980; Betti, 2011), more competitive, than C. peregrina; 3) the two which stated that the presence of these nudibranchs species showed a less photophilous lifestyle than is principally in shallower waters, in well-lit areas. that usually reported in literature, since in this study Furthermore, differently from Betti (2011) who both were found in a deeper bathymetric range; 4) reported the presence of both species particularly in if our hypotheses are correct, F. affinis and C. summer in the area of Conero (Adriatic Sea), we peregrina are warm-water species and their strong noticed that both species in the investigated areas presence in cold seasons might be used as an can be present with peaks in any seasons of the year. indicator of the increase in the seawater This different trend could be explained by two temperature. hypotheses. On one hand, since Sicily belongs to the southern sectors of the Mediterranean Sea, the seawater temperature is usually warmer than the REFERENCES Adriatic Sea. Indeed, in the Ionian Sea the seawater temperature fluctuates between 14–23°C, while in Ballesteros M., 1980. Contribución al conocimiento de the Adriatic Sea the seawater temperature ranges los Sacoglosos y Nudibranquios (: from 11°C to 23°C (Lejeusne et al., 2009). Opisthobranchia). Estudio anatómico, sistemático y Therefore, since in the cited literature (Ros, 1975; faunistico de las especies del mediterráneo español. Barletta & Melone, 1976; Ballesteros, 1980; Betti, Tesis Doctoral, Universidad de Barcelona: 46 pp. Ballesteros M., Madrenas E. & Pontes M., 2012-2020. 2011) F. affinis and C. peregrina are present “Flabellina affinis” in OPK-Opistobranquis, principally during summer, they seem to be warm- Published: 17/05/2012, Accessed: 04/08/2020 at water species. Consequently, in the Ionian coast of (https:// opistobranquis.info/en/uGvW0). Sicily these species could settle in any period of the Barletta G. & Melone G., 1976. Nudibranchi del year, while in the Adriatic Sea the settlement might promontorio di Portofino (Genova). Natura, 67: 203– occur in summer, because of the colder winter 236. seawater temperature. On the other hand, in the last Bavestrello G., Puce S., Cerrano C., Zocchi E. & Boero decades, we are experiencing a general increase in N., 2006. The problem of seasonality of benthic the seawater temperature of the Mediterranean Sea, hydroids in temperate waters. Chemistry and Ecology, 22 (supplement 1): S197–S205. https:// caused by the global warming (Bianchi et al., 2018). doi.org/10.1080/027575406006 70810 In fact, a 30-year data set (1974–2005) from the Betti F., 2011. Il regno dei nudibranchi, guida ai Spanish Catalan coast, revealed a clear warming molluschi opistobranchi della Riviera del Conero. La trend at four different depths from the surface to 80 Mandragora Editrice, Imola, 200 pp. m, with an impressive warming of 1.4 °C at 20 m Bianchi C., Caroli F., Guidetti P. & Morri C., 2018. (Lejeusne et al., 2009). Also in the Aegean Sea, Seawater warming at the northern reach for southern satellite sea surface temperature data from the last species: Gulf of Genoa, NW Mediterranean. Journal 20 years showed a significant 1 °C warming trend of the Marine Biological Association of the United (Lejeusne et al., 2009). Therefore, since F. affinis Kingdom, 98: 1–12. https://doi.org/10.1017/S00253 15417000819 and C. peregrina are probably warm-water species, Boero F., 1984. The ecology of marine hydroids and the presence of them in any season of the year could effects of environmental factors: a review. Marine be an indirect indicator of the warming of the Ecology, 5: 93–118. Mediterranean Sea. Catra M., Giaccone T., Giardina S. & Nicastro A., 2006. In conclusion, through the present study new Il patrimonio naturale marino bentonico della Timpa data on the seasonality and lifestyles of F. affinis di Acireale (Catania). Bollettino dell’Accademia and C. peregrina along the central-eastern coast of Gioenia di Scienze Naturali, 39 (366): 129–158. Sicily has been reported. These results were Clark K. B., 1975. Nudibranch life cycles in the Northwest Atlantic and their relationship to the interesting since reported information on these two ecology of fouling communities. Helgo Einderwiss species different from the cited literature:1) both Meeresunters, 27: 28–69. https://doi.org/10.1007/ species along the Ionian coasts of Sicily may be BF01611686 present in any season of the year with a high Di Silvestro D., Garzoli L. & Lodola A., 2010. number of specimens; 2) F. affinis along the Ionian Colonization status of the Mediterranean Sea by New data on the seasonality of Flabellina affinis and Cratena peregrina (Nudibranchia) in the Ionian Sea 1053

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